If you haunt eBay; you will occasionally find a used Tamron 90mm f/2.8 Macro (the lens previous to the present one that Tamron is distributing). Although this lens is not touted to be specifically designed for digital work (as is the 90mm f/2.8 Macro that Tamron is presently distributing) the image quality is outstanding and is right up there with my 24-70mm f/2.8L and 70-200mm f/4L IS lenses. You can usually find these lenses going for anywhere from $100-250. I got mine in mint condition for $100 plus a few bucks for shipping. It is in mint condition and provides outstanding imagery. The bokeh is top-notch and creamy. This bokeh and the f/2.8 aperture alongwith the 90mm focal length makes the Tamron a wonderful portrait lens as well as a great macro (focusing down to 1:1 without adapter) lens.
Although I have not personally used the Phoenix (AKA Cosina, Vivitar, Voigtlander, and very possibly Pentax) 100mm f/3.5 macro lens, I have read good reviews of its image quality. The build apparently leaves something to be desired but, the price, at somewhere around a hundred bucks - new, is very low.
http://www.nikonians.org/html/resources/non-nikon_articles/phoenix/100f35-1.html
http://www.phoenixcorp.com/Lenses/Auto_Focus_Lenses/AF_100mm_f_3_5_Macro/af_100mm_f_3_5_macro.html
You cannot effectively use Canon FD lenses with EOS cameras but, older Nikon, Pentax and possibly other brand manual focus macro lenses can be used with adapters and are usually dirt cheap. No problem not having AF, I usually use manual focus when shooting macros anyway. The adapters are generally cheap also.
I once had a Series One Vivitar f/2.5 (not the less expensive and less capable f/2.8 variety) Macro lens for my Pentax MX camera that had outstanding image quality. It used an adapter to get 1:1 imagery but was a great lens. This Series One Macro lens was produced for many different type of camera mounts and if you could find one that could adapt to an EOS mount camera, it would be an excellent and low cost option.
Another way to get really big (usually 1:1 or greater) imagery is to use a 50mm manual focus lens reversed on a 50mm Canon lens. The manual 50mm lens can be a canon, Nikon or just about any other brand. These lenses are often available for $10-15 and the reverse adapter ring can be had very inexpensively on eBay.
You just need to have the filter size of your lens and the filter size of the lens which you are going to reverse. Reverse rings are available in all sorts of combinations.
http://photography.search.ebay.com/reverse-ring_Lens-Accessories_W0QQcatrefZC6QQcoactionZcompareQQcoentrypageZsearchQQcopagenumZ1QQfgtpZQQfposZ97321QQfromZR2QQfsooZ1QQfsopZ1QQftrtZ1QQftrvZ1QQlopgZQQsabfmtsZ1QQsacatZ78998QQsadisZ200QQsaprchiZQQsaprcloZQQsargnZQ2d1QQsaslcZ2QQsbrftogZ1QQsofocusZbs
--
Retired Navy Master Chief Photographer's Mate. I was a Combat Cameraman, Motion Picture Director, and a Naval Aircrewman. I also had experience in reconaissance and intelligence photography. I have had considerable commercial photo experience in weddings and advertising photography. I am fully retired now although I dabble occasionally in dog portraiture. I presently use Canon DSLR cameras.